CN110062492A

CN110062492A - PWM light modulation with reduced audible noise

Info

Publication number: CN110062492A
Application number: CN201810053199.2A
Authority: CN
Inventors: 刘洋; 熊坤
Original assignee: Landes Vance
Current assignee: Landes Vance
Priority date: 2018-01-19
Filing date: 2018-01-19
Publication date: 2019-07-26
Anticipated expiration: 2038-01-19
Also published as: US20190230759A1; US10728982B2; DE102019101234A1; CN110062492B

Abstract

This application provides the method and apparatus of the PWM light modulation for LED light.The LED light includes one or more LED and the LED lamp driver for operating the LED.The described method includes: generating pwm signal；And the pwm signal is provided to the LED lamp driver；Wherein, the pwm signal includes the mixing of two or more different frequencies.

Description

PWM dimming with reduced audible noise

Technical Field

The invention relates to a method for PWM dimming of an LED lamp and a PWM dimming device for an LED lamp driver.

Background

With the advent of LED lamps (LEDs are an abbreviation for light emitting diodes), efficient, safe and long-life lighting devices are available. Like other light sources, the brightness of LEDs can be adjusted by dimming (dimming). For this purpose, different techniques for dimming lamps have been developed, including analog or linear dimming and PWM dimming (PWM is the abbreviation for pulse width modulation). Compared to the method of linear dimming, PWM dimming has advantages such as high efficiency and high precision and no CCT drift (CCT is an abbreviation of correlated color temperature).

However, PWM dimming may result in audible noise from the inductor and capacitor of the LED lamp driver operating at the PWM frequency. The inductor and capacitor of the LED lamp driver resonate at the PWM frequency, which in turn may cause vibration of other components, such as the printed circuit board of the LED lamp driver.

To reduce noise during PWM dimming, the LED lamp driver may be isolated from sound and/or vibration (potting). Alternatively, low noise components may be used. However, these solutions may require additional cost and space to be effective.

Disclosure of Invention

It is an object of the present invention to provide a method for PWM dimming of an LED lamp and a PWM dimming arrangement for an LED lamp driver, which are capable of reducing audible noise, preferably in an efficient and/or cost-effective manner.

This object is solved by a method and a PWM dimming arrangement according to the independent claims. Preferred embodiments are given by the dependent claims, the description and the figures.

Accordingly, a method for PWM dimming of an LED lamp is provided. An LED lamp includes one or more LEDs and an LED lamp driver for operating the LEDs.

According to the method, a PWM signal is generated and provided to an LED lamp driver. The PWM signal may be a current for energizing the LED or a signal used as a basis for modulating the current for energizing the LED. Preferably, the PWM signal has a periodic waveform comprising an active (active) portion and an inactive (non-active) portion in time. The brightness of the LED is adjusted by selecting or modifying the PWM duty cycle, which is the fraction (fraction) of the time period in a cycle (i.e., the time it takes the PWM signal to complete a switching cycle) that the signal is active (relative to the time period in which the signal is inactive).

According to the method, the PWM signal comprises a mixture of two or more different frequencies.

The above-described method for dimming an LED lamp significantly reduces audible noise when dimming an LED lamp, compared to a method using a conventional PWM signal having a single frequency. Noise reduction is achieved by varying the PWM frequency in time. Thus, the implementation of the method does not result in significant additional costs. A PWM dimming device implementing the method can be produced in a cost-effective manner. Furthermore, the circuit layout (e.g., PCB layout) of the LED lamp driver does not need to be modified or updated.

Preferably, the PWM signal is generated by the MCU, which further simplifies the implementation of the method and increases flexibility, since the MCU facilitates the adjustment or modification of the frequencies making up the PWM signal.

Possible mixtures of frequencies with good noise reduction performance include one or more of the following: 1kHz, 2kHz, 4kHz and 8 kHz.

Further improvements can be obtained by varying the different frequencies randomly or quasi-randomly in time.

In view of the response time of the human ear, it is preferred that one or more changes in frequency occur over a period of 100ms to 150ms, preferably about 125 ms.

Furthermore, a PWM dimming arrangement for an LED lamp driver is provided. The PWM dimming apparatus includes a dimming circuit configured to generate a PWM signal and provide the PWM signal to the LED lamp driver. The PWM signal includes a mixture of two or more different frequencies.

All features disclosed with respect to the method for PWM dimming are also disclosed for the PWM dimming arrangement. In addition, the technical effects, preferred or optional features and technical contributions and advantages described in relation to the method for PWM dimming are similarly applicable to PWM dimming devices. This includes: the dimming circuit preferably comprises an MCU configured to generate a PWM signal.

Drawings

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Shown in:

fig. 1a shows a periodic PWM waveform with a frequency of 1 kHz. FIG. 1b shows the audible noise spectrum obtained for the 1kHz PWM waveform of FIG. 1a generated by the MCU.

Fig. 2a shows a PWM waveform containing a mixture of PWM frequencies. Fig. 2b shows the audible noise spectrum obtained for the PWM waveform of fig. 2a generated by the MCU.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Here, elements that are the same, similar, or have the same or similar effects have the same reference numerals in the drawings. A repetitive description of these elements may be omitted to prevent redundant description.

The drawings and the dimensional relationships between elements shown in the drawings should not be considered to be drawn to scale. Rather, individual elements may be shown with exaggerated dimensions to enable better illustration and/or better understanding.

Fig. 1a shows a typical periodic PWM waveform for dimming an LED lamp. In this example, the PWM waveform has a frequency of 1 kHz. The PWM waveform may be generated by an MCU (microcontroller unit), which may be part of an external device or part of an LED lamp driver for operating one or more LEDs. The LED is energized by supplying a current modulated according to the PWM waveform. The brightness of the LED is adjusted by modifying the PWM duty cycle, i.e., the fraction (fraction) of the time period in a cycle (i.e., the time it takes the PWM signal to complete a switching cycle) that the signal is active (relative to the time period in which the signal is inactive).

FIG. 1b shows the audible noise spectrum measured for the 1kHz PWM signal of FIG. 1a generated by the MCU. An electro-acoustic sound level meter based on IEC61672 was used to obtain the noise spectrum in fig. 1b (and fig. 2 b). The x-axis of the spectrum represents audible frequencies and the y-axis represents time-weighted sound levels determined by a sound level meter.

The noise spectrum in FIG. 1b reveals a peak audible noise of 22.5dB at a PWM frequency of 1 kHz.

To reduce noise generated by applying a PWM signal for dimming, fig. 2a shows a PWM waveform including a mixture of PWM frequencies. In the present example, a random change of the PWM frequency within a period of 125ms is performed. The frequency set illustratively includes f 1-8 kHz, f 2-1 kHz, f 3-2 kHz, and f 4-4 kHz. The time period during which one or more frequency changes occur may be modified; however, a time period of between 100ms and 150ms and preferably a time period of about 125ms is advisable, since this corresponds approximately to the response time of the human ear.

Fig. 2b shows the audible noise spectrum measured for the PWM signal of fig. 2a generated by the MCU. The x-axis represents audible frequencies and the y-axis represents time-weighted sound levels determined by a sound level meter.

The noise spectrum of fig. 2b reveals that there is no peak at a certain frequency. The mixing of the PWM frequencies helps to disperse the noise to a range of frequencies within the frequency spectrum. In particular, since 1kHz in this example occurs only at 2/7 x 125ms during the 125ms period, the noise at 1kHz in the spectrum of fig. 2b is significantly reduced compared to the spectrum of fig. 1 b. The maximum noise of about 18.4dB in this example occurs at 2 kHz.

The PWM dimming device for an LED lamp shown above significantly reduces audible noise when dimming the LED lamp. Only standard electronic components are required to implement the PWM dimming arrangement. In addition, noise reduction is achieved by varying the PWM frequency. Thus, implementation of the presented techniques for noise reduction does not incur significant additional costs. PWM dimming arrangements can be manufactured in a cost-effective manner. Furthermore, the PCB layout of the LED lamp driver does not need to be modified or updated.

The present invention is not limited by the description based on the embodiments. Rather, the invention encompasses any novel feature and any combination of features, in particular of features in the patent claims, even if this feature or this combination itself is not explicitly indicated in the patent claims or exemplary embodiments.

List of reference numerals

f1, f2, f3, f4 frequency

Claims

1. A method for PWM dimming of an LED lamp, wherein the LED lamp comprises one or more LEDs and an LED lamp driver for operating the LEDs, the method comprising:

generating a PWM signal; and

providing the PWM signal to the LED lamp driver; wherein,

the PWM signal includes a mix of two or more different frequencies.

2. The method of claim 1, wherein the PWM signal is generated by an MCU.

3. The method of claim 1, wherein the mix of frequencies comprises one or more of: 1kHz, 2kHz, 4kHz and 8 kHz.

4. The method of claim 1, wherein the different frequencies vary randomly in time.

5. The method of claim 1, wherein the one or more changes in the frequency occur over a period of 100ms to 150 ms.

6. The method of claim 5, wherein the one or more changes in the frequency occur over a time period of about 125 ms.

7. A PWM dimming apparatus for an LED lamp driver, wherein the PWM dimming apparatus comprises:

a dimming circuit configured to generate and provide a PWM signal to the LED lamp driver, and

the PWM signal includes a mix of two or more different frequencies.

8. The PWM dimming apparatus of claim 7, wherein the dimming circuit comprises an MCU configured to generate the PWM signal.

9. The PWM dimming apparatus of claim 7, wherein the mix of frequencies comprises one or more of: 1kHz, 2kHz, 4kHz and 8 kHz.

10. The PWM dimming apparatus according to claim 7, wherein the different frequencies randomly change in time.

11. The PWM dimming apparatus according to claim 7, wherein the one or more changes in the frequency occur within a period of 100ms to 150 ms.

12. The PWM dimming apparatus of claim 11, wherein the one or more changes in the frequency occur over a time period of about 125 ms.